1. Field of the Invention
The invention relates to a solar photovoltaic energy conversion apparatus, more particularly to a transparent conductive oxide (TCO) based hybrid solar cell device, which not only allows the transmission of visible sunlight but also can enhance the photovoltaic energy conversion efficiency.
2. Description of the Prior Art
The earliest development of the solar cell system can be traced back to 1954, which was invented and proposed by Bell Laboratory in the United States. Solar cell is a kind of solar photovoltaic energy conversion semiconductor devices that uses sunlight to generate electric power directly. By adding impurity substances into highly pure semiconductor materials, semiconductors with different property can be made. For example, boron can be added into silicon to form p-type semiconductor while phosphorus can be added into silicon to form n-type semiconductor. When p-type and n-type semiconductors are combined to form p-n junctions, electrons and holes, electric current, and, thus, electric power will be generated by exposing the reverse-biased p-n junctions to sunlight.
Though there are many kinds of solar cells, most of them are produced from materials such as crystalline silicon, amorphous silicon, III-V semiconductors, and II-VI semiconductors, etc. Solar cell systems made by the above-mentioned materials are of dark color and opaque, which means the transmittance of the solar cells to the visible light is extremely low. In addition, due to the optoelectronic characteristics of materials, solar cells made by the above-mentioned materials can only absorb sunlight within the wavelength range of the visible light. Thus, the solar photovoltaic energy conversion efficiency is unable to be enhanced effectively.
Solar cells can be classified as transparent solar cells and opaque solar cells. FIG. 1 shows the structure of the conventional transparent solar cell, which consists of a substrate 101, a buffer layer 102, a first transparent conductive layer 103, a second transparent conductive layer 104, and an anti-reflective protective layer 105. FIG. 2 shows the structure of the conventional opaque solar cell, which consists of a substrate 201, a buffer layer 202, a first transparent conductive layer 203, a first silicon layer 204, a second silicon layer 205, a second transparent conductive layer 206, and an anti-reflective protective layer 207.
In the above-mentioned transparent solar cells, the advantage of high visible light transmittance is gained at the expense of the solar photovoltaic energy conversion efficiency because less solar energy can be used to generate electric power when the visible part of sunlight is not absorbed by the transparent solar cells. Though the opaque solar cell does not have the visible light transparency feature, the solar photovoltaic energy conversion efficiency is higher than that of the transparent solar cell. Therefore, how to integrate the advantages of both kinds of solar cells has become an important research and development issue for the next generation solar cells.
In the known arts, there is a U.S. Pat. No. 6,294,722 about “Integrated Thin-Film Solar Battery”. Though multi-layers of transparent conductive oxide thin films are used, it is still the transparent solar cell with low solar photovoltaic energy conversion efficiency.
As of Taiwan Patent Number M279981 of “Semiconductor Sensitized Solar Cell”, though the transparent conductive oxide thin film is used in the solar cell, an electrolytic layer is also added into the cell structure. In addition to higher manufacturing cost, only opaque solar cell with no visible light transparency is formed.
Therefore, how to integrate the advantages of the transparent solar cells and the opaque solar cells and to further raise the solar photovoltaic conversion efficiency have become a feasible goal and challenge for the next generation solar cells.